The first parameter is mandatory, and identifies the name of the country, region, city, etc. A full list of available parameters can be found in Category:Country data templates. For example, Template:Country data Bulgaria is used when the name parameter is specified as Bulgaria. Many flags are also available via shortened "aliases", such as standard three-letter country codes as specified by ISO 3166-1 alpha-3, IOC, or FIFA. The list of available "aliases" is found in Category:Country data redirects. Many of these country codes could be considered obscure, so it is recommended to use the full country name.

variant

The second parameter is optional, and identifies a flag variant to be used instead of the standard flag. This is most often used for historical flags but can also be used to specify naval flags, sport-use flags, etc. The list of available flag variants for each country is documented on the specific page for the country data template. For example, Template:Country data Bulgaria includes a description of each of the available flag variations for Bulgaria. This parameter can be a named parameter (e.g.. "variant=1815"), or a positional parameter, always after the country name.

size

This parameter is optional, and is used to specify the maximum width and/or height of the flag image. This parameter is specified using standard image syntax.

Template:Flag is used to display a wikilinked name next to the flag. The displayed name will be the same as the parameter used with the template, but the link target will be the main article for the country (in these examples, Bulgaria).

Template:Flagcountry is also used to display a wikilinked name next to the flag. The displayed name will always be the same, regardless of whether or not a country code alias is used as the template parameter.